Volume 4 Number 10 (Dec. 2009)

A New Slack Reclaiming Algorithm for Real-time Systems

Wenzhi Chen, Qingsong Shi, Weifang Hu, Wei Hu and Sha Liu

College of Computer Science and Technology, ZheJiang University, HangZhou 310027, ChinaAbstract—Real-time applications are ubiquitous in generalpurpose
computing environments, while the real-time systems
are growing in complexity. Thus in these hybrid real-time
systems, schedulers must guarantee that all hard real-time jobs
be completed before their deadlines and improve QoS of soft
real-time tasks as much as possible. Towards this goal we have
proposed a new slack reclaiming algorithm for server-based
real-time systems, and have also implemented it in a real time
emulator (RTSIM). This algorithm, named HBASH, which
enhances the Constant Bandwidth Server (CBS) by slack
reclaiming, allocates slack generated from the running process
to the task that needs the slack most, and then this selected task
will be scheduled immediately. Hence the algorithm is able to
make full use of slack and reduce the response time of soft realtime
tasks as much as possible. In this paper, we proved that our
algorithm does not violate the schedulability of tasks, and we
also evaluated the performance of this algorithm. The
experimental results demonstrate that HBASH outperforms
other slack reclaiming algorithms and improves soft real-time
performance significantly.